1. Field of the Invention
The present invention relates to a relative-dielectric-constant measuring method and apparatus for measuring the relative dielectric constant of an insulation film formed on the surface of a substrate.
2. Description of the Background Art
One of the most difficult issues associated with finer interconnections in semiconductor devices is the process of interconnecting electronic circuits. A problem with finer interconnections in semiconductor devices is a time delay of electric signals. Thus, in recent years progress has been made in multilevel interconnect technology.
Between two multilevel interconnect lines, an interlayer insulation film (hereinafter simply referred to as an “insulation film”) is buried. The insulation film is evaluated from its various physical properties such as insulating properties, mechanical strength, thermal resistance, and relative dielectric constant. Among these, the most important physical property is the relative dielectric constant. The insulation film is desirable to have a low relative dielectric constant for device operation. However, it is known that damages caused to the insulation film by processes such as etching will increase the relative dielectric constant of the insulation film. Thus, the material for the insulation film is selected also from the viewpoint of easy processing and leakage properties, and on the other hand, a technique for measuring the relative dielectric constant of an insulation film becomes important.
As techniques for measuring the relative dielectric constant of an insulation film, for example, there are known a technique for forming a metal electrode on the surface of an insulation film, and a technique for bringing a metal probe into contact with the surface of an insulation film.
However, the technique for forming a metal electrode on the surface of an insulation film might cause changes in the properties of an insulation film due to heat generated during electrode formation, and the like. Also, this technique is destructive measurement, so the measurement is time-consuming.
On the other hand, the technique for bringing a metal probe into contact with the surface of an insulation film provides contact between the metal probe and the surface of an insulation film by way of a liquid metal such as mercury. Thus, there is no need to form a metal electrode on the surface of the insulation film, thus allowing easy and simple measurement. However, high-precision measurement is difficult because of an unstable contact area of mercury. Besides, the use of mercury that is harmful to the human body is also a problem.
In order to solve the aforementioned problems, non-contact measurement of the relative dielectric constant of an insulation film is desirable. As a technique for non-contact measurement of the relative dielectric constant of an insulation film, there is known a technique for applying charge to the surface of an insulation film by corona charging and then obtaining surface charge and potential at that time, thereby to obtain the relative dielectric constant of the insulation film. However, since the insulation film generally has a porous structure to reduce its relative dielectric constant, a large amount of charge applied to the surface of the insulation film will leak into the film. Thus, it is difficult to accurately calculate the relative dielectric constant of an insulation film through analysis that is based on the assumption that charge exists only on the surface of the insulation film.
That is, using either of the aforementioned measurement techniques involves difficulty in non-contact and accurate measurement of the relative dielectric constant of an insulation film.